Frequency measuring instrument



8 Sheets-Sheet 2 Filed Feb. 28, 1951 (inventor ROBERT L. CHASE GttomegxApril 27, 1954 R. L. CHASE FREQUENCY MEASURING INSTRUMENT 8 Sheets-Sheet3 Filed Feb. 28, 1951 FIG. 3.

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ROBERT L. CHASE Gttorneg 8 Sheets-Sheet 4 April 27, 1954 R. CHASEFREQUENCY MEASURING INSTRUMENT Filed Feb. 28, 1951 Snoentor ROBERT L.CHASE 3404/4 flm Gttofneg April 27, 1954 R. L. CHASE FREQUENCY MEASURINGINSTRUMENT Filed Feb. 28, 1951 8 Sheets-Sheet 5 V Q u NQN u I V \N u m au u "r n m mwm mg n Flll-Il'l I I I l I Ill-IL I I I I I I l I I I l l II I I l I I l I Ill- 3nventor ROBERT L. CHASE Gttorneg April 27, 1954 R.L. CHASE FREQUENCY MEASURING INSTRUMENT mosh PmmE Zmventor ROBERT L.CHASE 4 lfillllllllllllllllllllllllllllll I lllllllllllllllllli u n u eh S W w n u H 1 8 n n \%N n u u w u u b 4 n r|L :LiL||L IL Q m l i Fattorney April 27, 1954 R. CHASE FREQUENCY MEASURING INSTRUMENT 8Sheebs-Sheet 8 Filed Feb. 28, 1951 3nventor ROBERT L. CHASE (IttornegPatented Apr. 27, 1954 UNITED STATES PATENT OFFICE 2,677,104 FREQUENCYMEASURING INSTRUMENT Robert L. Chase, New York, N. Y., assignor to theUnited States of America as represented by the United States AtomicEnergy Commission Application February 28, 1951, Serial No. 213,193

4 Claims. 1

The present invention relates to a method and apparatus for accuratelymeasuring an unknown frequency.

Electronic oscillators are employed in a wide variety of instruments andapparatus in industry today. It is often necessary to measure thefrequency of these oscillators to insure the proper operation of theinstrument controlled thereby. When the oscillator is frequencymodulated, it is also necessary to measure the frequency at a particularinstant after the start of the modulation cycle. In the latter case, themeasurement must be made in a very short time interval as the frequencyis continuously varying.

It is accordingly an object of this invention to provide a new andimproved method and apparatus for the measurement of an unknownfrequency. I

Another object of the invention is to provide a new and improved circuitwhich will accurately measure a varying frequency at any particularinstant.

A further object of the invention is to provide a new and improvedcircuit for measuring an unknown frequency a very short time interval.

Still another object of the invention i to provide a new and improvedcircuit for measuring an unknown frequency which circuit is synchronizedwith the phase of the unknown frequency.

Other objects and advantages will be in part obvious and in part pointedout hereinafter.

More particularly, a preferred embodiment of the apparatus of thepresent invention comprises a source of standard oscillations,amplifying and I recording means for counting the number of the standardoscillations emitted in a specified time interval, a second amplifyingand recording means for counting the number of cycles of the unknownfrequency for said specified time interval, and means for controllingthe duration of the specified time interval.

The many objects and advantages of the present invention may best beappreciated by reference to the accompanying drawings, the figures ofwhich illustrate apparatus incorporating a preferred embodiment of thepresent invention and capable of carrying out the method of theinvention. In the drawings:

Figure 1 is a block diagram showing the power distribution from thepower suppl to the various circuits of the invention.

Figure 2 is a'block diagram showing the manner in which the signalvoltages are interconnected between the various circuits of the"invention.

Figure 3 shows the wave form of voltages at indicated positions in thevarious circuits of the invention and comprises sub-figures 3A to 3Hinclusive.

Figure 4 is a schematic wiring diagram of the pulse shaping circuit.

Figure 5 is a schematic wiring diagram of the gate circuit, the gatecontrol circuit and the coincidence trigger tube circuit used for thepulses derived from the unknown alternating current source.

Figure 6 is a schematic wiring diagram of the first five stages of therecording circuit used for the unknown frequency oscillations.

Figure 7 is a schematic wiring diagram of the sixth through twelfthstages of the recording circult used for the unknown frequencyoscillations and Figure 8 is a schematic wiring diagram of the pulsingcircuit in which the terminating pulse for the counting time interval isderived.

Referring now to certain of the drawings in detail, the operativefeatures of the disclosed units of which will later be described, thereis shown in Figure l a power supply H0 which has an external connectionI i to a standard alternating current source. The power supply Ill]furnishes unidirectional operation voltages l2, l3, l4, 16, ll, 18 andhas a common ground connection 19. The voltages I2, I 3 and M arepositive and i the values of these voltages decrease from the highestvoltage l2 to the lowest voltage M. The voltages I6, I! and 18 arenegative and the values of these voltages increase in negative valuefrom the least negative voltage iii to the most negative voltage 18.Also shown in Figure l are blocks representing the circuits of theinvention; namely, a pulse shaping circuit Ill, a gate circuit 20, agate control circuit 30, a coincidence trigger tube circuit 41!, asealer and pulser circuit 58, a source of standard oscillations such asa crystal oscillator 60, a second gate circuit 16, a second gate controlcircuit 86, a second coincidence trigger tube circuit 99, a secondscaling circuit I00 and a starting pulse generator I26. The distributionof the voltages supplied by the power supply I ID to the variouscircuits of the invention is shown schematically. A detailed discussionof the connections to the voltages will be given in the description orthe circuits herein below.

Figure 2 shows the over-all circuit in block form as in Figure l andshow the signal voltage connections between the circuits.

output load H3" connects the output of starting pulse generator I20 tothe gate control circuit 3%. Lead ii I is connected to the input of thepulse shaping circuit I0. An output lead II2 of the pulse shapingcircuit Ill is connected to the gate circuit 20. An output lead III; ofthe gate circuit 23 is connected in parallel to the scaling circuit 56,the coincidence trigger tube #36, the gate control circuit 36 and to thesecond coincidence trigger tube 96. A lead I I6 of the sealing andpulsing circuit 56 connects the output of circuit 50 to both coincidencetrigger tube circuits G0 and 36. nected to the output of coincidencetube circuit 56 by a lead H8 and is further connected to gate circuit 29by a lead I22. An output lead I 26 of gate control circuit as isconnected to the second gate circuit 16. An input lead I26 to gatecircuit 16 connects gate circuit 16 to the standard oscillator 69.connected to the second scaling circuit I06.

Figure 3 shows several time correlated voltage wave forms of voltages atvarious referenced positions throughout the circuits of the invention.Discussion of these voltages and their wave forms will be made in thedescriptions of the circuits.

In Figure 4, the input lead I II to the pulse shaper circuit IE) isshown connected to the control grid of a pentode type tube I5I through acouplin condenser I52. Bias for the control grid of tube I5I is suppliedby a resistance network connected between the positive voltage I2 andthe common ground connection I9. The resista lead I59. The anode of thistube I5I is connected to the positive voltage I2 through an anoderesistor I6I and inductor I62, and is further connected to the controlgrid of tube I56 by a coupling network I63 comprising a parallelconnected resistor I64 and condenser I65.

The control grid of tube I56 is connected to ground through a grid biasresistor I66. The remaining connections of tube I56 are as follows: Theanode is connected to the positive voltage I2 through an anode resistorI61 and inductor I68 and to ground through a difierentiating networkconsisting of condenser I66 and resistor I'M. A crystal rectifier I12 isconnected in parallel with resistor I1I. Output lead H2 is connected tothe junction point of condenser I69 and resistor I1I.

In operation the lead III supplies the pulse shaper circuit III with avoltage as shown on Figure 3- A. The pulse shaper circuit 56 transformseach cycle of this voltage into a positive pulse as shown on Figure 3-3.In detail, pulse shaper III operates on the principle of the well knownSchmitt trigger circuit. The bias voltages of tubes I5I and I56 arearranged so that normally, tube I5I is cut off and tube I56 isconducting. The conduction of current through tube I56 maintains thecathode of tube I5I at a relatively high positive voltage. This willsucceed in keeping tube I5I cut off until the potential of the controlgrid of tube I5I is raised sufnciently to overcome the cathode bias. thepositive half cycle of the wave shape shown on Figure 3-A. As thispositive voltage builds up on the grid of tube I5I a point is reachedwhere tube I5I will start to conduct. This will give rise to a negativepulse at the anode of tube I5I which The gate control circuit 36 i con-An output lead I28 of gate circuit 10 is This will occur on F pulse istransmitted to the control grid of tube I56 through coupling networkI63. Tube I56 is thereby cut off causing a positive pulse at its anode.This pulse is sharpened by the difierentiating network made up ofcondenser I69 and resistor I1I so that the pulse appearing on outputlead I I2 is shaped as shown in Figure 3-B.

When the amplitude of the positive half cycle applied to the controlgrid of tube I5I falls to a certain value, the pulse shaping circuitwill return to its normal state with tube l5I cut off and with tube I56conducting. The negative pulse that results at the anode of the tube I56when it starts to conduct does not appear on the output lead I I2 sincerectifier I12 shorts out all negative pulses across resistor I'II toground. The pulse shaping circuit In therefore emits one positive pulseon output lead II2 for every cycle of voltage appearing on input leadIII.

Referring now to Figure 5, lead H 2 as previously disclosed is adaptedto supply a voltage, such as shown on Figure 3-B, through coupling condenser I89 to the control grid of a pentode type tube I9I of gatecircuit 20. The control grid of the tube I9: is further connected tonegative voltage I6 through a grid bias resistor I92. The remainingconnections of the tube I9I are as follows: The cathode is directlyconnected to the common ground connection I9 by a lead I93, the screengrid is directly connected to the positive voltage I4 by a lead I94 andthe suppressor grid is connected to the output lead I22 of gate controlcircuit 30 through a coupling network I96. Coupling network I96 consistsof a parallel connected condenser I91 and resistor I36. The anode of thetube I9I is connected to the positive voltage I4 through a droppingresistor I99 and to the control grid of pentode type tube 2| I through acoupling condenser 2 I2. The control grid of the tube 2 II is furtherconnected to the common ground I9 through resistor 243. The remainingconnections of tube 2 I I are as follows: The cathode and suppressor aredirectly connected to the common ground I9 by a lead 2 I4 and the screengrid is directly connected to the positive voltage I4 by a lead 2I6. Theanode of tube 2II is connected to the positive voltage I4 through ananode resistor 2 I1 and to the control grid of cathode follower tube 2I8through a coupling condenser 2 I9. The control grid of the tube 2 I8 isfurther connected to the negative voltage I1 through a resistor HI and acrystal rectifier 222 connected in parallel. The screen and suppressorgrids of tube 2I8 are connected directly to the anode by lead 223. Theanode is connected to positive voltage I2 through dropping resistor 22%and to ground through condenser 226. The output lead IN is connecteddirectly to the cathode of the tube ZIB and the cathode is connected toground through cathode resistor 221.

In operation, the gate circuit 26 receives pulses on input lead II2 asshown on Figure 3-3 and transmits the pulses to output lead I M onlyduring the unknown frequency counting time interval. It also amplifiesand shapes the pulses. In detail, when the tube I9I is in condition toconduct, the receipt on its control grid of the positive pulse shown inFigure 3-3 gives rise to an amplified negative pulse at its anode. Thisnegative pulse is applied to the control grid of amplifier tube 2 IIthrough the diiierentiating network made up of condenser 2 I2 andresistor 2 I3. This pulse on the grid of tube 2| I gives rise toanamplified positive pulse at its anode, which pulse is applied to thecontrol grid of cathode follower 5. tube 2 I 8 through thedifferentiating network consisting of condenser 2I9 and resistor 22LWhen this positive pulse is applied on the control grid of tube 2 I8,the 'potential a'crosscathode resistor 22'! rises in the same manner asthe applied pulse. The resulting pulse across resistor 227 is applied tooutput lead lid; The waveshape' of this pulse is shown on Figure 34:";The rectifier 222 in parallel with resistor 22E removes any negativeportions of the voltage wave form applied to the control grid of tube2H3.

It is therefore seen that gate circuit 22 will emit an amplifiedpositive pulse on output lead I It for each positive pulse received oninput lead H2. As mentioned above, however, this is only true if gatetube I3! is in condition to conduct. This condition is controlled bygate control circuit 33 as described hereinbelow.

Gate control circuit 30 receives its input on input lead H3 which isconnected to the control grid of buife'r amplifier tube 23I through acoupling condenser 232; The control grid of the tube 23! is furtherconnected to the negative potential It through resistor 233. Theremaining connections or this tube 235 are as follows: the suppressorgrid is internally connected to the cathode which is directly connectedto the common ground I3 by lead 234; the screen grid is connected to thepositive potential i2 by lead 236 through dropping resistor 23?. Theanode is 53 directly connected to the anode of tube 238 by lead 239.

The suppressor grid of the tube 238 is internally connected to thecathode which is directly connected to the common ground I9 by a lead 3244. Further connections of tube 233 are as follows: the screen isconnected to the positive voltage I2 by lead 253 and dropping resistor23?. The control grid is connected to the negative voltage I8 through abias resistor 232 and is directly connected to output lead I22. Thecontrol grid is further connected to the anode of tube 223 through acoupling network 229. Network 243 comprises a parallel connectedcondenser 25! and resistor 252.

The anode of the tube 238 is connected to the positive voltage i2through anode resistor 24B and dropping resistor 237 and is furtherconnected to the control grid of tube 243 through a coupling network2414. Coupling network 244 consists of a parallel connected condenser243 and resistor 221. The remaining connections of tube 243 are asfollows: the control grid is connected to negative voltage it through abias resistor 253, the suppressor grid is internally connected to thecathode which is directly connected to ground by lead 254. The anode isconnected to positive voltage I2 through anode resistor 256 and droppingresistor 231 and is further connected to lead H8.

In operation,- the gate control circuit 39 receives a positive pulseinput on lead I I3 as shown on Figure 3-0. The circuit operates toprovide a rectangular voltage on output lead I22 as shown on Figure 3-D.In detail, tubes 23% and 243 and their associated elements of the gatecontrol circuit 33 are interconnected in the form of an electronicswitch or better known as a. flipfiop circuit. The tube 243 is normallyconducting and the tube 238 is normally nonconducting.

The action of the flip-flop circuit is conventional in that a negativevoltage impressed at the control grid of. the tube 243 causes this tubeto become nonconducting and the tube 233 to become conducting. To returnthe circuit to its grid places tube I 9! 6 normal operating condition;it is then necessary to impress a. negative voltage at the control gridof the tube 238. The negative pulse to initiate the flip-flop action isderived from the buffer amplifier tube 23L A positive pulse as shown onFigure -3-C is applied on input lead H 3 to the control grid of tube 23I. I

This starting pulse serves to mark the beginning of the timing intervalduring which the unknown frequency is to be measured. The'application'of this positive pulse at the control grid of tube 23!gives rise to a negative amplified pulse at the anode of tube 23L Thenegative pulse is applied to the control grid of tube 243 throughcoupling network 242; This initiates the flip-flop action causing tube243 to become nonconducting and tube 238 to become conductmg.

The positive pulse is derived from starting pulse generator I23 shown inblock form on Figure 2. Starting pulse generator 128 may be anyconventional apparatus which is adapted for synchronization with theinitiation of the frequency modulation cycle of a frequency modulatedoscillator, or which may operate at random for the measurement of fixedfrequencies. For example, a counter-chronograph or single-shotmultivibrator may be used, The anode of tube 223 increases in potentialwhen this tube is cut on as shown on Figure 3 D vertical line a. Thisincrease in potential is applied through coupling network 253 to theoutput lead 122. The gate control circuit 33 therefore provides anincrease in positive potential on the output lead l22 when the startingpulse is applied to input lead I I3. The increased potential remains onlead I22 until the flip-flop circuit of gate control 30 is restored toits normal condition with tube 243 conducting. This is accomplished in amanner to be set forth in detail later in the application.

The positive potential on lead I22 is applied to the suppressor grid oftube lSI in gate circuit 23 through coupling network I535. Theapplication of the positive potential to the suppressor in condition toconduct. The pulses being applied to input lead H2 will now betransmitted through the gate circuit 20 to output lead H4 in the mannerdescribed hereinabove. blocks the gate circuit 22 by keeping a lowpotential on the suppressor grid oftube I9I until the start of themeasuring interval when the flipflop action of tubes 238 and 243 isinitiated.

Also shown on Figure 5 is the coincidence trig ger tube circuit so.Input lead H3 is connected to the control grid of 'pentode type tube 26!through coupling condenser 252. The control grid is also connected tothe negative potential I6 through grid resistor 253. Input lead H4 isconnected to the suppressor grid of the tube 26! through couplingcondenser 264. The suppressor grid is also connected to the negativepotential I6 through resistor 236'. The remaining connections of thistube 261 are as follows: the anode is directly connected to output lead3 I8 and the cathode is directly connected to the common ground l9 bylead 231. The screen grid is connected to the common ground l9 throughcoirdense'r 259 and to the positive voltage I2 by lead 268 and droppingresistor 231.

In operation, coincidence trigger tube circuit 23 emits a negative pulseon outputlead I I8 when it receives a positive pulse inputon lead I It.{The positive pulse on lead I I6 is derived from sealer and pulser 53 atthe end of a predetermined num- The gate control circuit 30 accordinglyI ber of cycles of the unknown alternating current source and marks theend of the measuring interval. The positive pulse output of scaler 59 isshown on Figure B-H just after vertical line 6. The operation of thepulse forming portion or scaler 59 will be described below with respectto Figure 8.

In detail, in Figure 5, the control grid of the tube 229i receivespositive pulses on lead H4 as shown on Figure 3-F. These pulses arederived from gate circuit as described hereinabove. 'lhe application ofthese positive pulses on the control grid of tube 28! does not causethis tube to conduct as its suppressor grid is being kept at thenegative potential 13. This eiiectively blocks conduction in tube 281and prevents any output voltage from appearing on lead H8.

When the positive pulse shown on Figure 3H line e is applied to thesuppressor grid of the tube 261, the tube is unblocked and is incondition to conduct. The next positive pulse to be applied on lead H4to the control grid of tube 26: will be amplified and inverted therebycausing a large dition. This reduces the potential on output lead I22,as shown on Figure 3Dline 1, thereby blocking the conduction of tube I?in gate circuit 2!). The input pulses subsequently applied to thecontrol grid of the tube i9i will no longer pass through this tube andtherefore no more I pulses will be applied to scaler 58 on lead H4. ineffect, the output of gate control circuit 39 is a rectangular voltage,the beginning of which starts the counting operation and the endin orwhich terminates the operation.

Referring to Figure 6, input lead H4 is shown connected to the controlgrid of tube 28i through condenser 282. The control grid of tube 28! isconnected to the common ground connection it through grid resistor 283.The remaining connections of the tube 28l are as follows: the cathode isconnected to the ground connection i9 through lead 284, cathode resistor286 and bypass condenser 281. The anode is connected to the positivevoltage l3 through anode resistor 288 and is further connected to theanode of tube 289 through a crystal rectifier 29L The anode of the tube28! is also connected to the control grid of tube 292 through a crystalrectifier 293 and a coupling network 294. Coupling network 294 consistsof a parallel connected resistor 293 and condenser 291. The anode of thetube 292 is directly connected to the positive voltage l3 by a lead 298.The control grid of the tube 292 is connected to the ground connection!9 through grid resistor 299 and bypass condensers 3M and 382. Inparallel with condenser 392 are inductors 333 and 394 which are inseries with reset switch 306.

The control grid of the tube 292 is further connected to the cathode oftube 289 through crystal rectifier 3. The cathode of the tube 292 isconnected to ground through cathode resistor 312 and is further directlyconnected to the control grid of the tube 289 by lead 313. The cathodeof the tube 289 is connected to ground through resistors 314 and 286 andis further directly connected to the cathode of tube 3l6 by a lead 351.The control grid of tube 289 is connected to the control grid of tube3l6 through a resistor M8.

The anode of the tube 3l5 is connected to the positive voltage 13through an anode resistor 359 in parallel with the series connectedresistor 32! and glow discharge tube 322. The anode of the mind 09 isconnected to the positive potential l3 through anode resistor 323 andinductor 324 and is further connected to the control grid of tube 326through coupling network 321. Coupling net work 321 consists of parallelconnected condenser 328 and resistor 329. The control grid of the tubeis connected to the ground connection 15 through resistors 331 and 332and is further connected to the cathode of tube 289 through a crystalrectifier 333.

The anode of the tube 328 is directly connected to the positive voltagei3 by a lead 334. The cathode of the tube 326 is connected to the groundcomiection l9 through cathode resistor 335 and is further connected tothe control grid 01 the tube 331. The cathode of the tube 33! isconnected to ground through the bypass condenser 338 and furtherdirectly connected to the catnode oi the tube 289 by lead 339. The anodeor the tube 331 is connected to the positive voltage In through anoderesistor 34! and inductor 342 and is rurtner connected to the junctionpoint or crystai rectifier 293 and coupling network 2:4. The controlgrid of the tube 33: is connected to the common ground connection l9through condenser M13 and resistor 344.

i he output lead 346 is connected to the junction point betweencondenser 343 and resistor 344.

l he above described circuit is the first stage or the scaier circuit 58which is used to record the pulses shown on Figure 3-F appearing on leadm. the scaler 50 may consist or as many sta es as necessary for therecordation oi the unknown frequency pulses.

in the present embodiment a scale of 4096 will be described but it is tobe understood that more or less scaler stages may be used depending onthe number of cycles of the unknown Ire uenoy to be measured. Since thescaler 59 is shown as having a scale-of-two circuit, in order to obtaina measure of 4096 cycles, it is necessary to nave l2 stages, that is, 2to the 12th power.

in operation, the first stage of the scaler 5t emits one output pulse onlead 343 for every two input pulses appearing on lead H4.

The tubes 289 and 331 are the switch tubes of this stage. Normally oneof these tubes is conducting and the other nonconducting. Tube 292 is acathode follower tube connected between the control grid of tube 289 andthe anode of tube Tube 326 is a cathode follower tube connected betweenthe grid of tube 331 and the anode of tube 289. The operation of theswitch tubes 289 and 331 is controlled by the output at the cathodes ofthe cathode follower tubes 292 and 326.

In detail, the switch tubes 289 and 331 and their associated circuitelements are arranged so that switch tube 331 is conducting and tube 289is cut ofi. Maintenance of current flow through the tube 331 depends onthe grid bias supplied to the control grid of the tube 331 from thecathode resistor 338 of tube 326. As long as the tube 326 conductssufficiently, the positive voltage built up across the resistor 339 willmaintain tube 331 in a conducting state. When less current flows throughthe tube 326 the grid bias on the control grid of the tube 331 will fallto such an extent that the tube 331 will be cut off.

The conduction of the tube 32 9, in turn, depends I on the grid biasdeveloped at its control grid.

9,. Therefore. as a positive pulse appears on: the input lead H4 it willbeamplified and inverted by the buifer amplifier tube 28! giving rise toan amplified, negative pulse atithe anode of this tube. This negativepulse is applied toithe control grid of the tube 326 through rectifier2M and coupling network 321. The negative pulse applied to the controlgrid of the tube 323 reduces the current in this tube causing thevoltage established across the cathode resistor 33.6 to decrease. Ashereinabove described this will out off tube 331. When tube 331 is cutoff. a large positive pulse is developed at" its anode and is applied tothe control grid of the tube 232' through coupling network 294. Thiscauses tube 282 to increase conduction and gives-rise to an increasedpositive voltage across cathode resistor 3.!2. This positive voltage isapplied to the control grid of the tube 283 causing it to conduct. Theswitch tubes 289 and 331 will now remain in this stable state until thearrival of another positiveapulse at the input lead H4. Thepositivevoltagethat is applied to the control grid of the tube 289 is alsoapplied to the control grid of the tube SIS through the grid resistor 318. This causes the tube 3l6 to conduct and lights up the glow tube 322in the anode circuit of the .tube. The next positive pulse appearing atthe input lead iii will reverse the conduction conditions of the tubecutting off tubes 2.89 and 316 and initiating current flow in tube 331.It should also be noted that the positive pulse that initiated currentflow through the tube 331 will also be applied on output lead 346through condenser 3 33. In order to tell which condition the first stageof the sealer 50 is in, it is merely necessary to see whether the glowtube 322 is on or on. As described hereinabove tube 322 will light upwhen tube 283 is conducting and will be oil when tube 283 is cut off.

It is accordingly seen that for every two input pulses appearing on leadH4 one output pulse appears on lead 346. Also glow tube 322 will lightup every second pulse. In order to obtain our preferred scale of 409.6it would be'possible to have 12 stages all similar to the first stagedescribed above. However, under normal operating frequencies it wouldnot be necessary to employ quite so large a scale. The switching actionof the first stage of: the sealer 5G is par-- tieularly fast and istherefore well adapted to be used directly with the incoming unknown.frequency pulses. However, as the pulses p'rcgres. through the varioussealer stages the required switching operation speed becomes less andless.

The above describedscaler stage is therefore used for the first fivestages and" a more conventional scale, known to the art astheHiginbotham sealer, used for the next seven stages, the operation ofwhich will be described below. The pulses progress through the secondthrough fifth stages in exactly the same manner as in the first stage.Conductor 346 is applied to the'buifer amplifier tube of the secondstage in the way that lead I H5 is applied .to amplifier tube 215i inthe first stage. Lead 331, at the bottom of the Figure 6 is alsoconnected to the switch tubes of the following stages in the mannershown. Lead. 331 is used for resetting all the sealer stages to zero ina manner to be described later.

The output of the fifth sealer stage appears on lead 341 whichcorresponds to lead 349 of the first stage. Referring to- Figure 7, thepulses appearing. on. lead: 341-2113 apriliedto: the control I; anode ofthe tube 363.

grid of the cathode follower tube 348 through coupling condenser 349.The control grid of the tube 348 is also further connectedto the commonground connection 19 through resistor'35l. The remaining connections ofthe tube 348 are as follows: the anode is directly connected to thepositive voltage 13 by a lead 352. The cathode is connected tothecommon' ground connection l9 through cathode resistor 353 and isfurther connected to the control grid of tube 354 through couplingcondenser 356'.

The control grid of the tube 3'54 is: connected to the ground connectionI9'thro11gh' resistor 351 and the cathode is connected to the commonground 59 through cathode resistor. 358 and bypass condenser 359. Thecathode of the tube 353 is further connected to the positive voltage l2through resistor 36!. The anode of thistube 354 is connected to thepositive voltage 12 through anode resistor 362 and is further connectedto theanode of tube 353 and the anode of tube 33-ithrough separatehalves of'the double diode tube 366.

The anode of the tube 363 is connected to the positive voltage 12through anode resistor 361 which is connected in parallel with theseries connected resistor 3.68 and glow discharge tube 369; The anode ofthe tube 363 is further connected to the controlgrid of the tube.364through the coupling network 31!. Coupling networli'31l consists ofparallel connected resistor 312 and condenser 313.The"remainingconnections of the tube 363 are as follows: the cathodeisconnected to the common ground"!!! through cathode resistor 314 and isdirectly connected to the cathode of tube 364 by'lead 316.

The control grid of the tube 363 is connected to the common ground 19through resistor 311 and is further connected to theanocle of the tube364 through the coupling network 318. Coupling network 318 comprisesparaillel connected resistor 319 and condenser 38!. The cathode of thetube 364 is connected to the common ground i9 through resistor 314 andbypass" condenser 332. The control grid of the tube 364 is connected tothe common ground !9 through resistors 383- and 38 i and mounted inparallel with resistor 383 is reset switch 385. The anode-of the tube3E4 is connected to the positive voltage 12 through resistors 386 and381. An; output lead 388. is connected to the junetionpoint' betweenresistors 386 and 331.

The above-described circuit includes the sixth stage of thesealingcir'cuitln'the present embodiment as well as the coupling tubes.343 and 353 between the fifth" andt-hesixth stage. The function of thesixth stage is the same 'as that described for the first stage, namely;to emit one positive pulse on output lead 338 for every two pulsesappearing on input lead 331. However, the resolving time of the circuitneed not be as short since the time interval between pulses received oninput, lead 341 is much longer than the interval between, pulsesreceived oninput lead H4.

The operation of the sixth stage of sealer 53 is as follows: the switchtubes of the circuit are tubes 333 and 334. The tubes 363 and 354 andtheir associated circuit elements are arranged so that one of the tubesis out 01f when the other tube is conducting. Let us assume that tube383 is cut off and tube3fi3 is conducting. This means that the potentialat the anode of the tube 363 will be much lower. than the potential ofthe Afuositive input pu 356. The positive pulse applied to the controlgrid of the tube 354 increases the conduction current through this tubewith a resulting of the voltage at the anode'of the tube. The loweringof the anode voltage of the tube 354 causes the upper half of thecoupling diode 366 to start conducting resulting in the application ofthe lowered voltage to the anode of the tube 363 and to the control gridof the tube 354 through the coupling network 311.

It should be noted that the lower half of the coupling diode 366 doesnot conduct as its plate is connected to the anode of the tube 364 whichis at a lower voltage than the anode of the tube 363. The loweredvoltage at the control grid of tube 364 causes the conduction currentthrough this tube to decrease, resulting in a higher voltage at theanode of the tube 334. This higher voltage is applied to the controlgrid of the tube 393 through coupling network 318 and the regenerativeaction continues until the second stable state of the circuit is reachedwith tube 364 cut oil and tube 363 conducting.

The circuit will remain in this condition until the next positive pulseis reached on the input lead 341 at which time the action will bereversed cutting oii tube 363 and causing tube 364 to conduct. The glowdischarge tube 369 in the anode circuit of the tube 363 will light upwhen this tube starts to conduct due to the voltage across resistor 361.

The cessation of current flow in tube 354 gives rise to a positive pulseon the output lead 338 and when the reverse action occurs with tube 364starting to conduct, a negative pulse will appear at the output lead388. Therefore the sixth stage of the scaling circuit 50 will emit onenegative pulse for every two pulses appearing on input lead 341. Theseventh through twelfth stages of sealer 50 preferably are exactly thesame as the above-described sixth stage which is enclosed in the dottedline. The cathodes of the coupling diode to the seventh stage areconnected directly to output lead 380. Therefore when the positive pulseappears on output lead 388 it is not transmitted to the seventh stage.However, when the negative pulse appears on output lead 388, that istransmitted to the seventh stage.

Accordingly, for every two pulses appearing on input lead 341, one pulsewill be transmitted to the seventh stage of the sealer. No couplingtubes such as 348 and 354 are necessary between succeeding stages asthey were inserted to provide a high impedance output for the fifthstage which was the type of circuit described above for Figure 6. Theoutput pulses of each succeeding stage are applied to the input of thefollowing stage. As shown in Figure '1, the ninth, tenth, eleventh andtwelfth stages have additional output leads 389, 391, 392 and 393,respectively, which are connected to terminals 394, 396, 391 and 398,respectively, of selector switch 399. The common terminal 40! isconnected to output lead 402.

The switching actions of the various scaler stages can continue up untilthe last or twelfth stage when the 4,096th pulse will start conduction'in the last switch tube and give rise to a 12 negative pulse on theoutput lead 393. However, if it is desired, the output pulse of eitherthe ninth, tenth or eleventh stages may be obtained instead by operatingselector switch 399 to the proper terminal. Use of selector switch 399will be explained in more detail later in the application with respectto an illustrative example. Therefore the scaling circuit of Figure '7operates to emit a negative pulse on output lead 402.

Referring now to Figure 8, the pulsing circuit of the sealer and pulser50 is shown. A negative pulse derived as explained above with referenceto Figure 'Tis applied on lead 402 to the control grid of pentode-typetube 412 through the coupling condenser 413. The control grid of thetube 412 is also connected to the movable arm of potentiometer 414 whichin turn is connected in series with resistors 416 and 411. The entireresistance series combination is connected between the positive voltage12 and the common ground connection 19. The suppresser grid of the tube412 is internally connected to the cathode which is connected to thecommon ground 19 through cathode resistor 418. The cathode of the tube412' is also directly connected to the cathode of the tube 419 by lead421.

The remaining connections of the tube 412 are as follows: the screengrid is directly connected to the positive voltage 12 by lead 422. Theanode is connected to the positive voltage 12 through anode resistor 423and inductor 424 and is further connected to the control grid of thetube 419 through coupling network 426 and to the control grid of thetube 421 through condenser 428. Coupling network 426 comprises theparallel connected resistor 429 and condenser 431. The control grid ofthe tube 419 is also connected to the common ground terminal 19 throughresistor 432.

The remaining connections of the tube 419 are as follows: the suppressergrid is internally connected to the cathode. The screen grid is directlyconnected to the positive voltage 12 by lead 433 and the anode isdirectly connected to the positive voltage 12 by lead 434. In the tube421 the control grid is connected to the common ground 19 throughresistor 436. The screen grid, the suppresser grid and the anode are allconnected together by leads 431 and 438. The anode of the tube 421 isconnected to the positive voltage 12 through anode resistor 439 and isfurther connected to ground through condenser 441. The cathode isconnected to the common ground 19 through cathode resistor 442 and isfurther connected directly to the output lead 116.

The function of the above-described circuit is to emit one positivepulse on output lead 116 as shown on Figure 3-H, vertical line ewhenever it receives the negative pulse input on lead 402. In detail,this pulse circuit is the familiar Schmitt trigger circuit, theoperation of which was described with respect to Figure 4 above.

In the circuit illustrated in Figure 8, tube 412 is normallynonconducting and tube 419 is nor mally conducting. The negative inputpulse received on lead 402 is applied to the control grid of the tube412 through coupling condenser 413 This lowers the conduction throughtube 412 and gives rise to a higher voltage at its anode. This highervoltage is applied to the control grid of tube 419 through couplingnetwork 426. The switching action is over when tube 412 is cut off andtube 419 is conducting.

The cessation of current through the tube 412 gives rise to a positivepulse at=the anodetof the tube which pulse is applied to the controlgrid of the cathode follower tube 42'! through coupling condenser 428.The application of the positive pulse to the control grid of tube 42'!gives rise to a similar positive pulse across the cathode resistor 442which appears on output lead H5. This pulse appearing on output lead H6is the pulse referred to above with respect to the coincidence triggertube 49 of Figure ,5. This pulse unblocks tube 26! of Figure 5permitting the pulses arriving at the control grid of this tube on inputlead H4 to trigger the gate control circuit 30, thereby blocking tube19! of gate circuit 20. This pulse on output lead H6 therefore marks theend of the measuring time interval.

In the foregoing description the output pulse appearing on lead H6 wasinitiated by the output pulse coming from the scaling circuit of Figure7 through selector switch 399. It is apparent that the initiating pulsecould be taken from any of the previous stages and the selector switch399 permits selecting this pulse from either the ninth, tenth, eleventhor twelfth stages. For example, if the 512th pulse is desired to end themeasuring interval, the selector switch 399 is operated to connect thecommon terminal 40'! to terminal 389.

Referring again to Figure 2, the operation of the standard frequencycircuits can now be described. Gate circuit lil, gate control circuit35,

coincidence trigger tube circuit Si! are in all respects similar to gatecircuit 253, gate control circuit 5% and coincidence trigger tubecircuit to, respectively. Sealer we is the same circuit shown in Figures6 and 7 for scaler 59 except that there is no provision for obtaining anoutput pulse from this scaler circuit. That is, there is no selectorswitch provided.

The operation of the gate control circuit 38 is initiated by the pulsesappearing on lead IM as shown by the wave form on Figure 3-F, verticalline b. This initiates the switching action in gate control circuit atin the same manner as in gate control circuit 30 which was initiated bythe starting pulse on input lead 5 13. The switching action of gatecontrol circuit 81] gives rise to an output wave form of the'type shownin Figure 3-E, vertical line b. This serves the purpose of unblockingthe gate circuit ill in the same manner as gate circuit 21; wasunblocked by the output pulse on lead I22 shown on Figure 3-D, verticalline a.

The unblocking of the gate circuit 70 permits the standard pulses shownon Figure S-G emanating from the source of standard oscillations 59 onoutput lead 26 to be transmitted through the gate circuit it and beapplied on output lead 528 to the scaling circuit iflil. Scaling circuitiilil will therefore count these standard input p lses until the gatecircuit ii! is again blocked. The blocking of this gate circuit H3 isaccomplished by the pulse appearing on output lead 1 it of scalingcircuit to and shown on Figure 3-H, after vertical line c. This outputpulse which was described above as being applied to the coincidencetrigger tube circuit id is also applied to the coincidence trigger tubecircuit 99 and un blocks this trigger tube circuit in thesame manner asin coincidence trigger tube circuit 4i! to permit the input pulses onlead l M to be applied to gate control circuit 8i on output lead ill.The application of the pulses on lead I I! to gate control circuit 833switches this circuit back to itsnormal condition, reducing thepotential of the lead 12s as shown on Figure 3-E,-vertical line 7. Thegate circuit 70 is thereby blocked preiii l4 venting any more pulsesfrom reaching the scaling circuit I06.

In View of the foregoing it now will be apparcut that an importantobject of the invention is achieved, namely that in order to determinethe unknown frequency it is merely necessary to compare the reading onthe glow discharge tubes of scaling circuit 5!] to the reading on theglow discharge tubes of the scaling circuit i063.

Consider now the operation of the invention as a unit rather than asindividual circuits as described above. To illustrate the accuracy andease of operability of the apparatus of the present invention anillustrative example will be worked out and traced through the entirecircuit. Assume that the frequency of an alternating current source inthe neighborhood of two megacycles is to be measured. If a five mgacycle standard oscillator is used and it is desired to obtain anaccuracy of 0.1% the counting interval must include at least 1000 cyclesof the standard oscillator. This is because the inherent accuracy of theapparatus is plus or minus one cycle of the known frequency. Thisaccuracy is limited by the fact that the frequency of the unknownalternating current source may be as much as plus or minus one cycle outof phase with the standard frequency when the measuring time interval isinitiated.

Therefore, to include at least 1000 cycles of the standard frequencyapproximately 400 cycles of the unknown frequency must be measured. Theselector switch 399 of Figure '7 is set to operate from the output ofthe ninth stage. That is, common terminal lfll. of selector switch 399is connected to terminal 394. We will thereby count 512 cycles (thefirst integral power of 2 greater than 400) of the unknown alternatingcurrent source. With the power supply I It energized the necessaryoperating voltages are supplied to the individual circuits as shown onFigure 1.

The glow discharge tubes of the scaling circuit 50 are extinguished andthis circuit is cleared by operating reset switches 3G6 and 385 ofFigures 6 and 7, respectively. Operating switch 396 of Figure 6 removesthe effective short from across resistor'332. This provides anadditional positive bias to the grid of the tube 326 derived from thegrid bias network made up of resistors 832, 33!, 329 and 323 connectedin series be tween the positive voltage l3 and the common groundconnection I8. The additional positive bias causes tube 326 to increaseconduction which in turn results in the conduction of the tube 33? andthe cessation of current fiow through tubes 289 and 3P5.

Similarly, in Figure 7, the second switch tube 364 is made to conduct byoperating switch 385 to remove the short across resistor 384. The gridbias network is here made up of resistors 384, 383, 312 and 35?connected in series between the positive voltage I2 and the commonground connection 19. Similar switches are operated to clear scalerlist.

With lead it! connected to the output of the unknown alternating currentsource, a wave shape such as shown on Figure 3-A is impressed on thepulse shaping circuit H3. The unknown frequency oscillations areimpressed on the con trol grid of the tube l5l. When the positiveportion of the wave shape is reached the switching action of the Schmitttrigger circuit will take efiect causing tube 15! to conduct and tube156 to be cut off. This gives rise to a positive pulse shown on Figure3-B at the anode of the tube (56. These pulses are transmittedthrough'the differentiating networl-z'made up of condenser I59 andresistor iii to output lead H2 which applies them to the control grid ofthe tube is! in gate circuit 20.

The pulses will not pass through tube iSl because the low potential onoutput lead 22 (indicated on Figure 3-D, prior to vertical line a) isimpressed on the suppressor grid of the tube i9! effectively blockingconduction in that tube. When the starting pulse shown on Figure 34.,vertical line a, is applied to the gate control circuit 36 on input leadH3 the resulting negative pulse at the anode of the tube 23! initiatesthe flip-flop action of the electronic switch tubes 238 and 253. Thiscauses tube 238 to start conducting and cuts off tube 293.

The cessation of current fiow through the tube 243 gives rise to a morepositive potential at its anode, which potential is applied to theoutput lead I22 through the coupling network 2 39. The start of therectangular voltage on output lead [22, shown on Figure 3-D, verticalline a, is applied to the suppressor grid of the tube Hi i. This permitsthe tube (9! to amplify the input pulses appearing at its control grid.These pulses are subsequently amplified by the tube 2 l i and passthrough the cathode follower tube 253 to output lead H4. put lead H4 isshown on Figure S F. These pulses are applied on lead EM to fourseparate circuits of the invention, namely the coincidence trigger tubecircuits do and 98, the scaling and pulsing circuit 59 and the gatecontrol circuit Bil.

Arrival of the pulses on input lead H5 at the coincidence trigger tubecircuits does not affect these circuits as the tubes are maintained inblocked condition due to the negative potential from lead l6 applied totheir suppresser grids. The application of the pulses of lead lid to thecontrol grid of the buffer amplifier tube in the gate control circuit 3of Figure 2 causes the the electronic switch tubes in that circuit toswitch to their second stable state in a fashion similar to that of gatecontrol circuit 38. The switching action of the gate control circuit 3"results in a higher potential on output lead I in a similar manner tothat described for output lead 22 of gate control circuit 30.

The higher positive potential oc urring on. output lead i2 3, shown onFigure 3-E, vertical line b, is applied to the gate circuit F9. Thearrival of the higher po itive potential on lead I24 unblocks the firsttube of the gate circui.

I6 and allows the standard oscillation arriving on input lead I25 to beamplified and shaped in gate circuit 16. These pul es shown on Figure3-G are applied on output lead I23 to caling circuit I99. Scalingcircuit illfi will record the e pulses until gate circuit 15 is againblocked.

The pulses occurring on out ut lead H4 are also applied to the controlgrid of the tube ZBI in scaling circuit 553, Figure 6. The fir t stagewill emit one negative pulse on output load 34% for every two positivepulses appearing on lead H4. This action will continue through thesuccessive stages of scaling circuit until the fifth stage where thenegative pulses will be applied on lead to emit one pulse to thesuccessive stage for every two pulses received. This operation willcontinue until the 512th pulse. which will acti The wave shape of thepulses on out- 'vate'the ninth stage of the scaling'circuitiifl.

The negative output pulse from this stage instead of being applied tothe tenth stage will be applied on lead 389 to terminal 394 of selectorswitch 399. From here it will be applied on lead 4132 to the controlgrid of the tube M2, Figure 3. This will cause the cessation of currentflow in tube M2 and the initiation of current flow in tube 419 therebygiving rise to a positive pulse at the anode of the tube M2. This pulseis transmitted through the cathode follower tube 421 to the output leadH6 and is shown on Figure 3-H, after vertical line e.

The application of the pulses on lead H8 to the coincidence trigger tubecircuits 40 and will unblock these tubes and permit the pulses occurringon input lead H S to be amplified and to reach the gate control circuits30 and 80 respectively. Gate control circuit 30 will switch back to itsnormal operating condition causing a decrease in the potential on outputlead I22 as shown on Figure 3-D, vertical line f. This will block thegate circuit 20 and prevent any further pulses from reaching the scalingcircuit 59. Similarly the operation of the gate control circuit 88 willlower the potential on the output lead !24 as shown on Figure 3-12,vertical line f and block the gate circuit 10 to prevent the pulsesoccurring on lead [26 to reach the scaling circuit I00.

In the foregoing manner scaling circuit 50 has recorded the oscillationsof the unknown alternating current source during the time intervalbetween the starting pulse input on lead I I3 and the stopping pulse onlead H6 represented by Figure 3-D, vertical lines a and f respectively.Also the scaling circuit I00 has recorded the standard oscillationsbetween the time of the appearance of the starting pulses on lead I I4and the stopping pulse on lead H6 represented by Figure 3-13, verticallines I) and 1 respectively. It is now merely necessary to prepare thereadings of the two scaling circuits in the following manner. If scaler109 has recorded 1299 pulses, the unknown frequency, 1, could bedetermined from the following equation:

The above equation would be true if there were no time delay in thescaling circuit of Figures 6 and 7. Actually in the twelve stage sealerdescribei in the embodiment. a signal is delayed approximately 7.8microseconds in its passage through the scalar. It is therefore possiblethat scaling circuit 50 has recorded 517 pulses instead of 512. Thiswould mean that four additional pulses had passed through the gatecircuit 20 while the 512th puls v was passing through the scaler 50 tothe ninth stage. The next pulse 17th) actuated the trigger tube circuits40 and S!) to turn off the gate circuits 20 and 19 respectively.Therefore if the scaling circuit had recorded 1299 counts the unknownfrequency actually would have been It can be seen that the frequencymeasuring interval for the above example lasted only 1300 cycles out of5 million cycles per second of the source of standard oscillations. Thisis equivalent to a measuring interval of only 260 microseconds and,despite the delay in the sealers, both sealers Stand I00 count cyclesfor measuring megacycles .9861 i .0015 me.

nter al wh h differ" nratie vb r e s han 0.2 microsecond". These,counting intervals, are.

representedon FisureB-Dmetween verticallirfe's aandf for sealer Ell; andbetween. vertical lines I). and-ion,Figure3 Eforscalerlllll It isaccordingly seen-,that the subject method and apparatus can easily beused for measuring thafrcau ncyiofcfrcduencymodula cdsimulato at anyrequired instant, after the start of the modulation cycle. If thefrequency in the above example was obtained from a frequency modu latedoscillator the frequency-for the neXt time interval couldbe obtainedbyrepeating theabove operation and allowing scaler- 5ii-to register 102i pulses (the tenth stage) before it-emits theoutput pulse for stoppingoperations. The differ..- ence between the frequency for 512 countsobtained above and the frequency for 1024 counts gives the frequencyvariation over this latter time period. Also, the frequency variationover the entire modulation cycle can be obtained by going through theentire range of scaler 50 and obtaining the differences betweensuccessive counts.

An alternative method for using the apparatus with frequency modulatedoscillators would be to change the time of initiation of the startingpulse with respect to the initiation of the modulation cycle.

The instrument is particularly applicable for :5

measuring the variation of the frequency modulated oscillator used inconjunction with a proton synchrotron for controlling the accelerationof the protons as they travel in an orbit about the synchrotron track.In one such application the apparatus can be used throughout a largefrequency range as the number of scaling stages in scalers 50 and I00can be extended and the standard oscillator 60 can be chosen to give thehighest accuracy with respect to the unknown frequency to be measured.

While the salient features of this invention have been described indetail with respect to one embodiment it will of course be apparent thatnumerous modifications may be made within the spirit and scope of thisinvention and it is therefore not desired to limit the invention to theexact details shown except insofar as they may be defined in thefollowing claims.

I claim:

1. Apparatus for measuring the frequency of a frequency-modulatedoscillator during an interval of its modulation cycle which comprises incombination, a source of standard oscillations of higher frequency thansaid frequency-modulated oscillator, amplifying and recording means forregistering the number of standard oscillations occurring during saidinterval, pulse forming means for developing a pulse of voltage for eachoscillation of said frequency-modulated oscillator, means for countingand recording each of said pulses occurring during the counting timeinterval and means for synchronizin the initiation and cessation of thecountin time interval with the oscillations of said frequency-modulatedoscillator.

18 2 Apparatus for measuring the frequency .of a frequency-modulated.oscillator during anine reii f mo u atiq circle. hich p n cs, in.combination, meansgdev eloping a'pulse of volt-' sel r ic irbn zed with.the, oscillations of said frequencymodulated oscillator, a gage controlen ive o id qlt se ii lssfan c: reignin ag ctaneul r. a tase. a gat c uire; sponsiveto. said.rectangularvoltage and-said oscillationsand deve opn an tputpu se of v tasaie s ch'qisaig c c t en e ns fo c u means, fec'othe; numberof said output th coun i g,timei rval. a d; ermin nepu seiatl to develop 'a' pulse of voltage operable on said gate control circuitto reduce said rectangular voltage and thereby blocking said gatecircuit, a source of standard oscillations, of higher frequency thansaid frequency-modulated oscillator, amplifying means for said standardoscillations and recording means for registering the number of standardoscillations occurring during said counting time interval.

3. Apparatus for measuring the frequency of a frequency-modulatedoscillator during an interval of its modulation cycle which comprises incombination, means developing a, pulse of voltage synchronized with theoscillations of said frequency-modulated oscillator, a gate controlcircuit responsive to said voltage pulse and developing a rectangularvoltage, a ate circuit responsive to said rectangular voltage and saidoscillations and developing an output pulse of voltage for each of saidoscillations, means for countin the number of said output pulses and fordeveloping a terminating pulse of voltage at the end of the countingtime interval, means respon- Site to said terminating pulse and theoutput pulses of said gate circuit and developing a pulse of voltageoperable on said gate control circuit to reduce said rectangular voltagethereby blocking said gate circuit, a source of standard oscillations ofhigher frequency than said frequencymodulated oscillator, a, second gatecontrol circuit responsive to the output voltage of said gate circuitdeveloping a rectangular voltage, a second gate circuit responsive tosaid last mentioned rectangular voltage and said standard oscillationsand developing a standard output pulse for each of said standardoscillations, means for counting said standard pulses and meansresponsive to said terminating pulse for blocking said second gatecircuit.

4. Apparatus for measuring the frequency of a frequency-modulatedoscillator during an interval of its modulation cycle which comprises incombination, a startin pulse generator for developing a pulsesynchronized to the oscillations of said frequency-modulated oscillator,a gate control circuit connected to said pulse generator and developinga rectangular voltage in response to the synchronized pulse, a gatecircuit connected to said frequency-modulated oscillator and to saidgate control circuit, said gate circuit generating an output pulse ofvoltage for each of said oscillations to be measured, a first sealercircuit for counting and registering the number of said generated outputpulses and for developing a voltage pulse at the end of a predeterminednumber of registered pulses, a coincidence trigger tube connected to theoutput of said first sealer and to the output of said gate circuit, saidtrigger tube reversing the conduction veloping a terminating pulse'of dn er e; rfs iasat cir itandadap esi,

19 conditions of said gate control circuit in response to said scalerdeveloped pulse, said gate control circuit thereby reducing saidrectangular voltage and extinguishing the output from said gate circuit,a second gate control circuit connected to the output of said first gatecircuit for developing a rectangular voltage, a second gate circuit, asource of standard oscillations of higher frequency than saidfrequency-modulated oscillator, said second gate circuit being connectedto both the output of the second gate control circuit and the standardoscillation source and developing a voltage pulse for each of saidstandard oscillations, a second sealer circuit connected to the outputof said second gate circuit for counting and registering said secondsate circuit developed 20 voltage pulses during the counting timeinterval and a second coincidence trigger tube connected to the outputof said first gate circuit for reversing the conduction conditions ofsaid second gate control circuit whereby the output of said second gatecircuit is extinguished.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,405,597 Miller Aug. 13, 1946 2,455,639 Anderson 1 Dec. '7,1948 2,510,485 Vossber June 6, 1950 2,516,189 Dinsmore July 25, 19502576,90!) Brockman Nov. 27, 1951

